rfc2124.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Network Working Group                                          P. Amsden
Request for Comments: 2124                                      J. Amweg
Category: Informational                                        P. Calato
                                                              S. Bensley
                                                                G. Lyons
                                                  Cabletron Systems Inc.
                                                              March 1997

     Cabletron's Light-weight Flow Admission Protocol Specification
                              Version 1.0

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

Abstract

   Light-weight Flow Admission Protocol, LFAP, allows an external Flow
   Admission Service (FAS) to manage flow admission at the switch,
   allowing flexible Flow Admission Services to be deployed by a vendor
   or customer without changes to, or undue burden on, the switch.

   Specifically, this document specifies the protocol between the switch
   Connection Control Entity (CCE) and the external FAS. Using LFAP, a
   Flow Admission Service can: allow or disallow flows, define the
   parameters under which a given flow is to operate (operating policy)
   or, redirect the flow to an alternate destination. The FAS may also
   maintain details of current or historical flows for billing, capacity
   planning and other purposes.

Table of Contents

1.  Introduction ..................................................    2
2.  Message Flows .................................................    3
3.  Message Contents and Format ...................................    4
     3.1.  IE Formats .............................................    5
     3.2.  Flow Admission Request (FAR) Message ...................   14
     3.3.  Flow Admission Acknowledge (FAA) Message ...............   15
     3.4.  Flow Admission Update (FAU) Message ....................   15
     3.5  Flow Update Notification (FUN) Message ..................   16
     3.6.  Flow Update Acknowledge (FUA) Message ..................   16
     3.7.  Flow Change Request (FCR) Message ......................   17
     3.8.  Flow Change Acknowledge (FCA) Message ..................   17
     3.9.  Administrative Request (AR) Message ....................   18
     3.10.  Administrative Request Acknowledge (ARA) Message ......   18
4.  Error Handling ................................................   18



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RFC 2124                          LFAP                       March 1997


     4.1.  FAA Related Error Handling .............................   19
     4.2.  FUA Related Error Handling .............................   19
     4.3.  FCA Related Error Handling .............................   19
     4.4.  ARA Related Error Handling .............................   20
5.  Security Considerations .......................................   20
6.  Author's Addresses ............................................   20
7.  References ....................................................   21

1.  Introduction

   Light-weight Flow Admission Protocol, LFAP, allows an external Flow
   Admission Service (FAS) to manage flow admission at the switch,
   allowing flexible Flow Admission Services to be deployed by a vendor
   or customer without changes to, or undue burden on, the switch. It
   provides a means for network managers, or management systems, to
   establish connection admission parameters for multiple switches in a
   single management domain by configuring policy information and other
   data via a single centralized connection admission control point.

   Specifically, this document specifies the protocol between the switch
   Connection Control Entity (CCE) and the external FAS. Using LFAP, a
   Flow Admission Service can: allow or disallow flows, define the
   parameters under which a given flow is to operate (operating policy)
   or, redirect the flow to an alternate destination. The FAS may also
   maintain details of current or historical flows for billing, capacity
   planning and other purposes.

   A significant advantage of this protocol is that it relieves switch
   vendors from the complexity of policy enforcement under any number of
   policy representation schemes. Similarly, switch configuration
   managers do not need to translate organization-determined policy or
   usage procedures, limitations and guidelines into an arbitrarily
   large set of vendor-specific representations. Finally, use of such a
   scheme makes possible plug-and-play connection management at the
   present time - in the absence of a standardized representation for
   connection policies.

   This document describes the message flow between switch CCE and FAS,
   the messages used and error handling that applies. This constitutes
   the LFAP interface definition.











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2.  Message Flows

   Initiating message flows between CCE and FAS entities always
   originate at the switch.  Therefore, the switch is the point at which
   connectivity is originated.  The CCE must have IP reachability using
   some approach described elsewhere (e.g.  [1577] or [LANE]) and an IP
   address for the FAS must be preconfigured at the switch CCE.  The CCE
   establishes TCP connectivity using the registered port number - ###.

   As shown below, Flow Admission Request (FAR) messages are sent by a
   switch's Call Control Entity (CCE) to the Flow Admission Service
   (FAS). These messages are sent when a flow is about to be set up by
   the switch and contain specific information relating to the flow -
   such as flow identifier, source/destination and qualifying
   information about the flow - that may be required to determine the
   admissibility of the flow and any operating policies that apply to
   the flow if it is admitted.

   The FAS responds with a Flow Admission Acknowledge (FAA) message (to
   the CCE) with a status indicating connection admissibility and any
   operating policy information that applies to the flow.  If a FAA
   message contains mandatory operating policies that the switch CCE
   does not understand, the switch would abort the flow using the Flow
   Admission Update (FAU) message.

    ,--------------------.            ,--------------------.
    |        FAS         |            |       Switch       |
    |                    |            |        CCE         |
    `--+----+----+-------'            `------+-----+----+--'
     ^ | ^  ^ |  ^ |  ^ ^              ^ ^  ^ |  ^ |  | ^ |
     | | |  | |  | |  | |     AR       | |  | |  | |  | | |
     | | |  | |  | |  | '--------------' |  | |  | |  | | |
     | | |  | |  | |  |       ARA        |  | |  | |  | | |
     | | |  | |  | |  '------------------'  | |  | |  | | |
     | | |  | |  | |          FUA           | |  | |  | | |
     | | |  | |  | `------------------------' |  | |  | | |
     | | |  | |  |            FUN             |  | |  | | |
     | | |  | |  `----------------------------'  | |  | | |
     | | |  | |               FCR                | |  | | |
     | | |  | `----------------------------------' |  | | |
     | | |  |                 FCA                  |  | | |
     | | |  `--------------------------------------'  | | |
     | | |                    FAU                     | | |
     | | '--------------------------------------------' | |
     | |                      FAA                       | |
     | `------------------------------------------------' |
     |                        FAR                         |
     `----------------------------------------------------'



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RFC 2124                          LFAP                       March 1997


   When a connection is established, periodically during the course of
   maintaining the connection and when a change in connection state
   occurs, the switch CCE sends a Flow Update Notification (FUN) message
   to the FAS.  The FAS, in turn, responds with a Flow Update
   Acknowledge (FUA) message with a Flow failure code if a an error
   condition has been detected. An example of error conditions would be
   receipt of a FUN message indicating octets received and sent for a
   connection never admitted.

   The FAS may send a Flow Change Request (FCR) to the CCE either to
   effect a change in the state of a specific connection or to set any
   new/changed policy information that applies to the flow.

   The CCE replies with a Flow Change Acknowledge (FCA) message and may
   respond  with a flow failure code indicating the offending flow or
   policy change.

   Either the CCE or the FAS may initiate a Administrative Request (AR).
   The CCE uses it to get a Flow Identifier Prefix. The FAS uses it to
   request FUN messages be returned on some set of flows.

   The requested entity (FAS or CCE) replies with a Administrative
   Request Acknowledge. The FAS uses the ARA to return the requested
   Flow Prefix. The CCE uses the ARA to return any Flow Identifiers that
   were in error on the AR.

3.  Message Contents and Format

   LFAP defines nine messages: "Flow Admission Request", "Flow Admission
   Acknowledge", "Flow Admission Update", "Flow Update Notification",
   "Flow Update Acknowledge", "Flow Change Request", "Flow Change
   Acknowledge", "Administrative Request" and "Administrative Request
   Acknowledge" (FAR, FAA, FAU, FUN, FUA, FCR, FCA, AR, ARA
   respectively).

   FAR messages are sent by a switch call control entity (CCE) to the
   Flow Admission Service (FAS). FAA messages are responses from the FAS
   to the CCE. FUA messages are responses from the CCE only under error
   conditions. FUN messages originate at switches and are acknowledged
   by FUA messages from the FAS. FCR messages are sent by the FAS to the
   CCE and are acknowledged by FCA messages. AR messages are sent by
   either the Entity (FAS or CCE) and are acknowledged by the ARA
   messages.








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RFC 2124                          LFAP                       March 1997


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Version    |    Op Code    |   Reserved    |    Status     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Message ID           |         Message Length        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                 Information Element (IE) Fields               ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The general message format for all LFAP messages is as shown above.
   Version is 1 and Op Codes are as follows:

             FAR - 1
             FAA - 2
             FAU - 3
             FUN - 4
             FUA - 5
             FCR - 6
             FCA - 7
             AR  - 8
             ARA - 9

   The Status field serves as a Status on the overall message. The
   values that Status may assume are:

          STATUS:
             SUCCESS   = 0
             CORRUPTED = 1
             VERSION   = 2

   Message ID is used to associate each original message with its
   corresponding response and must be unique for the combination of
   sender and responder while an original message is pending. The
   Message Length excludes the 8 octets of the message header.

3.1.  IE Formats

   IE fields consist of 2-octet TYPE, 2-octet LENGTH and a variable
   length VALUE sub-fields. All IEs are even multiples of 4 octets in
   length, left-aligned and zero filled if necessary. Length is computed
   excluding the 4 octet TYPE and LENGTH fields.

   Individual IEs are formated as described in following sections.





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Byte Count IE

   Contains the count of octets sent and received associated with the
   identified connection. IE format is:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         TYPE = 1 or 2         |          LENGTH = 16          |